1. The Field of the Invention
This invention relates to sensor devices and, more particularly, to novel systems and methods for sensing the position and/or movement of an object in multiple degrees of freedom.
2. The Prior Art
In the operation of electrical and electro-mechanical systems, it is often necessary or desirable to detect and/or continuously monitor the position, movement, and/or orientation of an object. Such sensing and/or monitoring is, in fact, essential for the proper operation of many such systems.
For example, pressure gauges and strain gauges commonly use the position of an object as an indication of pressure or strain. Such a gauge might include a membrane or other member which is deflected in accordance with the pressure or strain being experienced. Accordingly, the gauge must necessarily include some means for detecting the position of the membrane or other member such that the pressure or strain can be accurately determined.
Similarly, accelerometers and gyroscopes typically use the position, movement, and/or orientation of some internal member to detect and measure acceleration and/or a change in orientation. An accelerometer may, for example, include a member which is displaced from some reference position whenever the accelerometer experiences an acceleration. In such cases, the accelerometer also requires a means for detecting the magnitude and direction of the displacement of the object, from which the magnitude and direction of the acceleration can then be determined.
A conventional phonograph also must include some type of device for sensing movement. As the phonograph needle travels along the grooves of a phonograph record, the needle vibrates in accordance with the sounds which have been stored on the record. Some type of device is thus required to detect the vibrations of the phonograph needle such that the vibrations can be converted into audible sounds.
The recent technological growth in the field of robotics and in the development of limb prostheses has given rise to an even greater need for various types of sensors. A sensor is, for example, often used to indicate that a robot or prosthetic limb has contacted or is "touching" an object. In many cases, it is desirable that the sensor also be capable of detecting the magnitude of the pressure which is being applied to the object. In addition, sensors are frequently used to monitor the position and orientation of each of the various component parts of a robot or prosthetic limb. The information obtained from all of the sensors is then provided to some type of control system.
In an effort to provide sensors suitable for use in applications such as those outlined above, those skilled in the art have developed a number of different kinds of devices for sensing position and/or movement. A few of the most common types of devices are described generally below.
Most of the early position sensor devices were mechanical in nature, and such devices are still in wide use today. In mechanical sensor devices, the object whose position or movement is to be sensed is typically physically connected to a pointer, a dial, or some other type of visual indicator. Movement of the object is thus transmitted mechanically to the pointer or dial. The position and movement of the pointer or dial is then periodically observed, and the position and/or movement of the object can thereby be determined.
While mechanical sensor devices are adequate for many applications, such devices are not well suited to automation since the "output" of such devices must generally be perceived visually. Accordingly, those skilled in the art have developed a number of sensor devices which instead provide some type of electrical output.
One relatively simple sensor device which provides an electrical output includes a capacitor which is coupled in some way to the object whose position and/or movement is to be sensed. The capacitor is typically coupled to the object in such a way that movement of the object changes the net electrical charge on the plates of the capacitor. For example, the object may be connected to one of the parallel plates of a capacitor, while the other plate of the capacitor remains fixed; the voltage between the two plates of the capacitor is kept constant. Movement of the object thus changes both the distance between the plates of the capacitor and, as a result, the net electrical charge on each of the capacitor plates. Such a change in the net charge can then be detected and monitored using known high impedance amplifying and tuning circuitry.
Other prior art sensor devices which provide an electrical output detect the position and/or movement of an object using optics. Such optical sensor devices have a number of different configurations.
For example, an optical sensor device may include a light source which is attached to or reflected from the object whose position is to be sensed. The device also includes one or more light-sensitive components, such as, for example, photocells, photodiodes, lateral effect photodiodes, or photoconductive sheets or layers of some sort. The light-sensitive components are appropriately positioned around the object to be sensed so as to interact with the light emanating or reflected from the object. The electrical output response of the light-sensitive components is then used to provide an indication of the position and/or movement of the object.
A prior art optical sensor device might also be configured as an interferrometer. Basically, an interferrometer is a device which can be used to measure changes in distance with a high degree of accuracy by detecting phase/amplitude relationships resulting from interacting light waves.
For example, light emanating from a coherent light source may be split into two separate beams. One beam is then reflected from a mirror which is attached to the object whose position is to be sensed, and the other beam is reflected from a stationary mirror. The two beams are then recombined into a single beam. The recombined beam will have certain phase/amplitude characteristics which are dependent upon the relative distance which was traveled by the two beams separately. A light-sensitive component, such as those identified above, is then used to detect such phase/amplitude characteristics in the recombined beam, the output of the light-sensitive component providing an indication of any changes in the object's position.
Some prior devices have included radioactive sensors to detect and monitor position. In one such device, which comprises an accelerometer, a radioactive sphere is positioned within a chamber. Radioactive particles emanating from the sphere are detected by a pair of beta-sensitive diodes located behind a slit system. The intensity of the beta radiation on the diodes is used to indicate the position of the sphere within the chamber.
RADAR and SONAR techniques are also widely used in the prior art to detect position and/or movement. Using such techniques, radio or sound waves are first transmitted toward an object. The radio or sound waves which are reflected by the object are then analyzed in order to determine the position and/or movement of the object.
Despite the sophistication and number of the prior art sensor devices available, the prior art devices and methods suffer from a number of significant disadvantages.
For example, prior art sensor devices are generally limited to detecting position, movement, and/or orientation of an object in only one degree of freedom. That is, the prior art devices and methods are typically limited to sensing position and movement in only one dimension, such as along a particular line. Consequently, in order to use the prior art devices and methods to detect motion in multiple degrees of freedom (such as, for example, to fix the position of an object in three-dimensional space), a cumbersome and expensive support structure is generally required which will accommodate the placement of numerous sensors at various positions spacially around an object.
Most prior art sensor devices are also relatively complex and require elaborate support systems in order to function properly. This is particularly true in the case of the optical sensor devices described above. The complexity of the prior art devices and methods increases the likelihood that such devices and methods will malfunction. Such complexity also significantly increases the cost of manufacturing and using the prior art devices.
In addition, the prior art sensor devices are generally relatively large. In many cases, however, it is desirable to use sensor devices which are very small. Such is particularly the case, for example, in the fields of robotics and of limb prostheses. In these fields of application, the large size of the sensor devices is often a significant disadvantage and can significantly hinder the effective development and operation of robotic and prosthetic apparatus.
Another disadvantage of the prior art sensor devices described above is that they are not well suited for use in association with semiconductors. It is well known that light will modify the performance characteristics of semiconductors. Therefore, if semiconductor technology is to be used in connection with the prior art sensor devices, potentially expensive and tedious shielding must generally be provided in order to protect the semiconductor elements from exposure to light.
Further, while it is often desirable to use a sensor device in association with some type of integrated circuitry, the prior art sensor devices are typically not well adapted for use with conventional integrated circuits. Most prior art sensor devices cannot be manufactured using conventional integrated circuit technology. Such sensor devices cannot, therefore, be readily manufactured in direct association with integrated circuits but must be manufactured separately and thereafter connected to the desired integrated circuits. As a result, the cost of manufacturing and assembling the prior art sensor devices in association with integrated circuits is significantly increased.